Method of generating a reactive species and polymer coating applications therefor

ABSTRACT

A polymer coated fiber, a polymer-coated web, and a method of coating a fiber or a web. The fiber or web is coated with a composition comprising an admixture of unsaturated polymerizable material and a photoreactor, and the composition on the fiber or web is irradiated with an amount of radiation sufficient to cure the composition and form a coating on the fiber or web. The photoreactor comprises a wavelength-specific sensitizer covalently bonded to a reactive species-generating photoinitiator. Suitable wavelength-specific sensitizers have a molar extinction coefficient greater than about 5000 liters per mole per cm at an absorption maximum and resulting photoreactors have a quantum yield of greater than about 0.5 at an absorption maximum. Suitable photoreactors include 2- p-(2-methyllactoyl)phenoxy!ethyl-1,3-dioxo-2-isoindolineacetate, 2-hydroxy-2-methyl-4&#39;- 2- p-(3-oxobutyl)phenoxy!ethoxy!propiophenone, 4- p- (4-benzoylcyclohexyl)oxy!phenyl!-2-butanone, and 1,3-dioxo-2-isoindolineacetic acid diester with 2-hydroxy-4&#39;-(2-hydroxyethoxy)-2-methylpropiophenone.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a division of application Ser. No. 08/327,077, filedOct. 21, 1994, now abandoned, which is a continuation-in-partapplication of U.S. Ser. No. 08/268,685, filed on Jun. 30, 1994, nowabandoned.

BACKGROUND OF THE INVENTION

The present invention relates to a method of generating a reactivespecies. The present invention also relates to radiation-initiatedpolymerization and curing processes. For convenience, much of thediscussion which follows centers on free radicals as a particularlysignificant reactive species. Such discussion, however, is not to beconstrued as limiting either the spirit or scope of the presentinvention.

Polymers long have served essential needs in society. For many years,these needs were filled by natural polymers. More recently, syntheticpolymers have played an increasingly greater role, particularly sincethe beginning of the 20th century. Especially useful polymers are thoseprepared by an addition polymerization mechanism, i.e., free radicalchain polymerization of unsaturated monomers, and include, by way ofexample only, coatings and adhesives. In fact, the majority ofcommercially significant processes is based on free-radical chemistry.That is, chain polymerization is initiated by a reactive species whichoften is a free radical. The source of the free radicals is termed aninitiator or photoinitiator.

Improvements in free radical chain polymerization have focused both onthe polymer being produced and the photoinitiator. Whether a particularunsaturated monomer can be converted to a polymer requires structural,thermodynamic, and kinetic feasibility. Even when all three exist,kinetic feasibility is achieved in many cases only with a specific typeof photoinitiator. Moreover, the photoinitiator can have a significanteffect on reaction rate which, in turn, may determine the commercialsuccess or failure of a particular polymerization process or product.

A free radical-generating photoinitiator may generate free radicals inseveral different ways. For example, the thermal, homolytic dissociationof an initiator typically directly yields two free radicals perinitiator molecule. A photoinitiator, i.e., an initiator which absorbslight energy, may produce free radicals by either of two pathways:

(1) the photoinitiator undergoes excitation by energy absorption withsubsequent decomposition into one or more radicals; or

(2) the photoinitiator undergoes excitation and the excited speciesinteracts with a second compound (by either energy transfer or a redoxreaction) to form free radicals from the latter and/or formercompound(s).

While any free radical chain polymerization process should avoid thepresence of species which may prematurely terminate the polymerizationreaction, prior photoinitiators present special problems. For example,absorption of the light by the reaction medium may limit the amount ofenergy available for absorption by the photoinitiator. Also, the oftencompetitive and complex kinetics involved may have an adverse effect onthe reaction rate. Moreover, commercially available radiation sources,such as medium and high pressure mercury and xenon lamps, emit over awide wavelength range, thus producing individual emission bands ofrelatively low intensity. Most photoinitiators only absorb over a smallportion of the emission spectra and, as a consequence, most of the lampsradiation remains unused. In addition, most known photoinitiators haveonly moderate quantum yields (generally less than 0.4) at thesewavelengths, indicating that the conversion of light radiation toradical formation could be more efficient. Thus, there are continuingopportunities for improvements in free radical polymerizationphotoinitiators.

SUMMARY OF THE INVENTION

The present invention addresses some of the difficulties and problemsdiscussed above by the discovery of an efficient method for utilizingradiation. Hence, the present invention comprehends a method ofgenerating a reactive species which includes providing awavelength-specific sensitizer in association with a reactivespecies-generating photoinitiator and irradiating thewavelength-specific sensitizer. Such method involves effectively tuningthe energy-absorbing entity, referred to herein as a polymolecularphotoreactor, to efficiently utilize an emitted band of radiation. Thewavelength-specific sensitizer effectively absorbs photons andefficiently transfers the absorbed energy to the photoinitiator which,in turn, generates a reactive species. The wavelength-specificsensitizer is adapted to have an absorption peak generally correspondingto a maximum emission band of the radiation source.

The association of a wavelength-specific sensitizer with a reactivespecies-generating photoinitiator results in a structure referred toherein for convenience as a polymolecular photoreactor. Thus, the methodof the present invention may be described as a method of generating areactive species which involves exposing a polymolecular photoreactor toradiation, in which the polymolecular photoreactor includes awavelength-specific sensitizer associated with a reactivespecies-generating photoinitiator.

The radiation to which the polymolecular photoreactor is exposedgenerally will have a wavelength of from about 4 to about 1,000nanometers. Thus, the radiation may be ultraviolet radiation, includingnear ultraviolet and far or vacuum ultraviolet radiation, visibleradiation, and near infrared radiation. Desirably, the radiation willhave a wavelength of from about 100 to about 900 nanometers. Moredesirably, the radiation will be ultraviolet radiation. e.g.,ultraviolet radiation having a wavelength of from about 100 to about 375nanometers. The radiation desirably will be incoherent, pulsedultraviolet radiation from a dielectric barrier discharge excimer lamp.

In its simplest form, the polymolecular photoreactor consists of asingle wavelength-specific sensitizer associated with a single reactivespecies-generating photoinitiator. In this instance, the photoreactorwill be a bimolecular photoreactor. However, the photoreactor mayinclude more than one wavelength-specific sensitizer and/or more thanone reactive species-generating photoinitiator. When the polymolecularphotoreactor is a bimolecular or trimolecular photoreactor and theradiation to which it will be exposed is ultraviolet radiation, thebimolecular or trimolecular photoreactor desirably will contain abenzoyl moiety and a moiety which is either a phthalic acid derivativeor a phenyl-substituted aliphatic ketone derivative.

The present invention also comprehends a method of polymerizing anunsaturated monomer by exposing the unsaturated monomer to radiation inthe presence of the efficacious polymolecular photoreactor describedabove. When an unsaturated oligomer/monomer mixture is employed in placeof the unsaturated monomer, curing is accomplished.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic representation of the excimer lamp employed inthe examples.

FIG. 2 is a series of plots of control photoinitiator and polymolecularphotoreactor concentration in an adhesive versus through-cure times(radiation exposure times for complete curing) for two controlphotoinitiators and four polymolecular photoreactors of the presentinvention.

FIG. 3 consists of plots of through-cure times for a controlphotoinitiator and a polymolecular photoreactor of the present inventionat a constant concentration in an adhesive versus film thickness.

DETAILED DESCRIPTION OF THE INVENTION

The term "polymerization" is used herein to mean the combining, e.g.covalent bonding, of large numbers of smaller molecules, such asmonomers, to form very large molecules, i.e., macromolecules orpolymers. The monomers may be combined to form only linearmacromolecules or they may be combined to form three-dimensionalmacromolecules, commonly referred to as crosslinked polymers.

As used herein, the term "curing" means the polymerization of functionaloligomers and monomers, or even polymers, into a crosslinked polymernetwork. Thus, curing is the polymerization of unsaturated monomers oroligomers in the presence of crosslinking agents.

The terms "unsaturated monomer," "functional oligomer," and"crosslinking agent" are used herein with their usual meanings and arewell understood by those having ordinary skill in the art. The singularform of each is intended to include both the singular and the plural,i.e., one or more of each respective material.

The term "unsaturated polymerizable material" is meant to include anyunsaturated material capable of undergoing polymerization. The termencompasses unsaturated monomers, oligomers, and crosslinking agents.Again, the singular form of the term is intended to include both thesingular and the plural.

The term "wavelength-specific sensitizer" is used herein to mean thatthe sensitizer is adapted to have an absorption wavelength bandgenerally corresponding to an emission peak of the radiation. Either orboth of the sensitizer and the radiation may have more than oneabsorption wavelength band and emission peak, respectively. In the eventboth the sensitizer and the radiation have more than one absorptionwavelength band and emission peak, respectively, the generalcorrespondence just described need not be limited to a single absorptionwavelength band and a single emission peak.

The term "quantum yield" is used herein to indicate the efficiency of aphotochemical process. More particularly quantum yield is a measure ofthe probability that a particular molecule will absorb a quantum oflight during its interaction with a photon. The term expresses thenumber of photochemical events per photon absorbed. Thus, quantum yieldsmay vary from zero (no absorption) to 1.

The term "reactive species" is used herein to mean any chemicallyreactive species including, but not limited to, free-radicals, cations,anions, nitrenes, and carbenes.

The term "associated" as used herein is meant to include any means whichresults in the wavelength-specific sensitizer and the reactivespecies-generating photoinitiator being in sufficiently close proximityto each other to permit the transfer of energy absorbed by thesensitizer to the photoinitiator. For example, the wavelength-specificsensitizer and the reactive species-generating photoinitiator may bebonded to each other or to a spacer molecule as described hereinafter bycovalent, hydrogen, van der Waals, or ionic bonds. Alternatively, thesensitizer and the photoinitiator may be physically admixed.

The method of the present invention involves generating a reactivespecies by exposing a polymolecular photoreactor to radiation in whichthe polymolecular photoreactor includes a wavelength-specific sensitizerassociated with a reactive species-generating photoinitiator. In otherwords, the method involves providing a wavelength-specific sensitizer inassociation with a reactive species-generating photoinitiator andirradiating the wavelength-specific sensitizer. The sensitizer absorbsphotons having a specific wavelength and transfers the absorbed energyto the photoinitiator which, in turn, generates a reactive species.However, the efficiency with which a reactive species is generated issignificantly greater than that experienced with the reactivespecies-generating photoinitiator alone. For example, the polymolecularphotoreactor desirably will have a quantum yield greater than about 0.5.More desirably, the quantum yield of the polymolecular photoreactor willbe greater than about 0.6. Even more desirably, the quantum yield of thepolymolecular photoreactor will be greater than about 0.7. Still moredesirably, the quantum yield of the polymolecular photoreactor will begreater than about 0.8, with the most desirable quantum yield beinggreater than about 0.9.

As stated above, the polymolecular photoreactor of the present inventionincludes a wavelength-specific sensitizer in association with a reactivespecies-generating photoinitiator. Any wavelength-specific sensitizerknown to those having ordinary skill in the art may be used in thepresent invention. Similarly, any reactive species-generatingphotoinitiator may be used which generates the desired reactive species.Examples of reactive species include, but are not limited to, freeradicals, carbenes, nitrenes, cations, and anions. Illustrated below areexamples of several of such species.

With regard to the free radical-generating photoinitiators, thesephotoinitiators may be any of the photoinitiators known to those havingordinary skill in the art. The largest group of photoinitiators arecarbonyl compounds, such as ketones, especially α-aromatic ketones.Examples of α-aromatic ketone photoinitiators include, by way ofillustration only, benzophenones; xanthones and thioxanthones;α-ketocoumarins; benzils; α-alkoxydeoxybenzoins; benzil ketals orα,α-dialkoxydeoxybenzoins; benzoyldialkylphosphonates; acetophenones,such as α-hydroxycyclohexyl phenyl ketone,α,α-dimethyl-α-hydroxyacetophenone,α,α-dimethyl-α-morpholino-4-methylthioacetophenone,α-ethyl-α-benzyl-α-dimethylaminoacetophenone,α,α-ethyl-α-benzyl-α-dimethylamino-4-morpholinoacetophenone,α-ethyl-α-benzyl-α-dimethylamino-3,4-dimethoxyacetophenone,α-ethyl-α-benzyl-α-dimethylamino-4-methoxyacetophenone,α-ethyl-α-benzyl-α-dimethylamino-4-dimethylaminoacetophenone,α-ethyl-α-benzyl-α-dimethylamino-4-methylacetophenone,α-ethyl-α-(2-propenyl)-α-dimethylamino-4-morpholinoacetophenone, or,α-bis(2-propenyl)-α-dimethylamino-4-morpholinoacetophenone,α-methyl-α-benzyl-α-dimethylamino-4-morpholinoacetophenone, andα-methyl-α-(2-propenyl)-α-dimethylamino-4-morpholinoacetophenone;α,α-dialkoxyacetophenones; α-hydroxyalkylphenones; O-acyl α-oximinoketones; acylphosphine oxides; fluorenones, such as fluorenone,2-t-butylperoxycarbonyl-9-fluorenone,4-t-butylperoxycarbonyl-nitro-9-fluorenone, and2,7-di-t-butylperoxycarbonyl-9-fluorenone; and α- and β-naphthylcarbonyl compounds. Other free radical-generating photoinitiatorsinclude, by way of illustration, triarylsilyl peroxides, such astriarylsilyl t-butyl peroxides; acylsilanes; and some organometalliccompounds. The free radical-generating initiator desirably will be anacetophenone.

Examples of carbenes include, for example, methylene or carbene,dichlorocarbene, diphenylcarbene, alkylcarbonylcarbenes, siloxycarbenes,and dicarbenes. Examples of nitrenes include, also by way of example,nitrene, alkyl nitrenes, and aryl nitrenes. Cations (sometimes referredto as carbocations or carbonium ions) include, by way of illustration,primary, secondary, and tertiary alkyl carbocations, such as methylcation, ethyl cation, propyl cation, t-butyl cation, t-pentyl cation,t-hexyl cation; allylic cations; benzylic cations; aryl cations, such astriphenyl cation; cyclopropylmethyl cations; methoxymethyl cation;triarylsulphonium cations; and acyl cations. Cations also include thoseformed from various metal salts, such as tetra-n-butylammoniumtetrahaloaurate(III) salts; sodium tetrachloroaurate(III); vanadiumtetrachloride; and silver, copper(I) and (II), and thallium(I)triflates. Examples of anions (sometimes referred to as carbanions)include, by way of example, alkyl anions, such as ethyl anion, n-propylanion, isobutyl anion, and neopentyl anion; cycloalkyl anions, such ascyclopropyl anion, cyclobutyl anion, and cyclopentyl anion; allylicanions; benzylic anions; aryl cations; and sulfur- orphosphorus-containing alkyl anions, Finally, examples of organometallicphotoinitiators include titanocenes, fluorinated diaryltitanocenes, ironarene complexes, manganese decacarbonyl, and methylcyclopentadienylmanganese tricarbonyl. Organometallic photoinitiators generally producefree radicals or cations.

The types of reactions that various reactive species enter into include,but are not limited to, addition reactions, including polymerizationreactions; abstraction reactions; rearrangement reactions; eliminationreactions, including decarboxylation reactions; oxidation-reduction(redox) reactions; substitution reactions; and conjugation/deconjugationreactions.

The other component of the polymolecular photoreactor is awavelength-specific sensitizer. Such sensitizer generally may be anycompound which, when associated with the reactive species-generatingphotoinitiator, absorbs photons having a specific wavelength andtransfers the absorbed energy to the photoinitiator. As a practicalmatter, two classes of compounds are known to be useful aswavelength-specific sensitizers, namely, phthalic acid derivatives andphenyl-substituted aliphatic ketones. A particularly useful example ofeach class is phthaloylglycine and 4-(4-hydroxyphenyl)butan-2-one,respectively.

As stated above, the polymolecular photoreactor of the present inventionis comprised of a wavelength-specific sensitizer in association with areactive species-generating photoinitiator. The sensitizer may be in asimple mixture with the photoinitiator, or it may be bonded to thephotoinitiator. For example, the sensitizer may be bonded to thephotoinitiator by covalent, hydrogen, van der Waals, or ionic bonds.Desirably, the sensitizer is covalently bonded to the photoinitiator.

As noted earlier, the wavelength-specific sensitizer is adapted to havean absorption wavelength band generally corresponding to an emissionpeak of the radiation. In addition, the wavelength-specific sensitizerwill have a high intensity of absorption. For example, thewavelength-specific sensitizer may have a molar extinction coefficientgreater than about 5,000 liters per mole per cm (lmole⁻ cm⁻¹) at anabsorption maximum. As another example, the wavelength-specificsensitizer may have a molar extinction coefficient (absorptivity)greater than about 10,000 lmole⁻¹ cm⁻¹. As a further example, thewavelength-specific sensitizer will have a molar extinction coefficientgreater than about 20,000 lmole⁻¹ cm⁻¹.

The absorption characteristics of the wavelength-specific sensitizer arenot limited to a single wavelength band. Many compounds exhibit morethan one absorption wavelength band. Consequently, a wavelength-specificsensitizer may be adapted to absorb two or more wavelength bands ofradiation. Alternatively, two or more wavelength-specific sensitizersmay be associated with a reactive species-generating photoinitiator.Such two or more wavelength-specific sensitizers may absorb the samewavelength band or they may absorb two or more different wavelengthbands of radiation.

In the embodiment where the wavelength-specific sensitizer is bound tothe reactive species-generating photoinitiator, any suitable method thatis known in the art may be used to bond the sensitizer to thephotoinitiator. The choice of such method will depend on the functionalgroups present in the sensitizer and photoinitiator and is readily madeby those having ordinary skill in the art. Such bonding may beaccomplished by means of functional groups already present in themolecules to be bonded, by converting one or more functional groups toother functional groups, or through one or more spacer molecules. Theterm "spacer molecule" is used herein to mean any molecule which aids inthe bonding process. For example, a spacer molecule may assist in thebonding reaction by relieving steric hindrance. Alternatively, a spacermolecule may allow use of more reactive or more appropriate functionalgroups, depending upon the functional groups present in the sensitizerand photoinitiator. It is contemplated that a spacer molecule may aid inthe transfer of energy from the sensitizer to the photoinitiator, byeither allowing a more favorable conformation or providing a morefavorable energy transfer pathway.

Exposing the polymolecular photoreactor to radiation results in thegeneration of a reactive species. Thus, the polymolecular photoreactormay be employed in any situation where reactive species are required,such as for the polymerization of an unsaturated monomer and the curingof an unsaturated oligomer/monomer mixture. The unsaturated monomers andoligomers may be any of those known to one having ordinary skill in theart. In addition, the polymerization and curing media also may containother materials as desired, such as pigments, extenders, aminesynergists, and such other additives as are well known to those havingordinary skill in the art.

By way of illustration only, examples of unsaturated monomers andoligomers include ethylene; propylene; vinyl chlorides; isobutylene;styrene; isoprene; acrylonitrile; acrylic acid; methacylic acid; ethylacrylate; methyl methacrylate; vinyl acrylate; allyl methacrylate;tripropylene gIycol diacrylate; trimethylol propane ethoxylate acrylate;epoxy acrylates, such as the reaction product of a bisphenol A epoxidewith acrylic acid; polyester acrylates, such as the reaction product ofacrylic acid with an adipic acid/hexanediol-based polyester; urethaneacrylates, such as the reaction product of hydroxypropyl acrylate withdiphenylmethane-4,4'-diisocyanate; and polybutadiene diacrylateoligomer.

As already noted, the radiation to which the polymolecular photoreactoris exposed generally will have a wavelength of from about 4 to about1,000 nanometers. Thus, the radiation may be ultraviolet radiation,including near ultraviolet and far or vacuum ultraviolet radiation:visible radiation: and near infrared radiation. Desirably, the radiationwill have a wavelength of from about 100 to about 900 nanometers. Moredesirably, the radiation will have a wavelength of from about 100 to 700nanometers.

Desirably, when the reactive species-generating photoinitiator is anorganic compound, the radiation will be ultraviolet radiation having awavelength of from about 4 to about 400 nanometers. More desirably, theradiation will have a wavelength of from about 100 to about 375nanometers, and even more desirably will have a wavelength of from 200to about 370 nanometers. For example, the radiation may have awavelength of from about 222 to about 308 nanometers. The radiationdesirably will be incoherent, pulsed ultraviolet radiation from adielectric barrier discharge excimer lamp.

When the wavelength-specific sensitizer is an organometallic compound,the radiation desirably will have a wavelength of from about 4 to about1,000 nanometers. More desirably, the radiation will have a wavelengthof from about 700 to about 900 nanometers. Even more desirably, theradiation will have a wavelength of from about 785 to about 825nanometers. Most desirably, the radiation will have a wavelength ofapproximately 800 nanometers.

Dielectric barrier discharge excimer lamps (also referred to hereinafteras "excimer lamp") are described, for example, by U. Kogelschatz,"Silent discharges for the generation of ultraviolet and vacuumultraviolet excimer radiation." Pure & Appl. Chem., 62, No. 9. pp.1667-1674 (1990); and E. Eliasson and U. Kogelschatz, "UV ExcimerRadiation from Dielectric-Barrier Discharges." Appl. Phys. B. 46, pp.299-303 (1988). Excimer lamps were developed by ABB Infocom Ltd.,Lenzburg, Switzerland, and at the present time are available fromHeraeus Noblelight GmbH, Kleinostheim, Germany.

The excimer lamp emits incoherent, pulsed ultraviolet radiation. Suchradiation has a relatively narrow bandwidth, i.e., the half width is ofthe order of approximately 5 to 100 nanometers. Desirably, the radiationwill have a half width of the order of approximately 5 to 50 nanometers,and more desirably will have a half width of the order of 5 to 25nanometers. Most desirably, the half width will be of the order ofapproximately 5 to 15 nanometers.

The ultraviolet radiation emitted from an excimer lamp can be emitted ina plurality of wavelengths, wherein one or more of the wavelengthswithin the band are emitted at a maximum intensity. Accordingly, a plotof the wavelengths in the band against the intensity for each wavelengthin the band produces a bell curve. The "half width" of the range ofultraviolet radiation emitted by an excimer lamp is defined as the widthof the bell curve at 50% of the maximum height of the bell curve.

The emitted radiation of an excimer lamp is incoherent and pulsed, thefrequency of the pulses being dependent upon the frequency of thealternating current power supply which typically is in the range of fromabout 20 to about 300 kHz. An excimer lamp typically is identified orreferred to by the wavelength at which the maximum intensity of theradiation occurs, which convention is followed throughout thisspecification and the claims. Thus, in comparison with most othercommercially useful sources of ultraviolet radiation which typicallyemit over the entire ultraviolet spectrum and even into the visibleregion, excimer lamp radiation is essentially monochromatic.

Excimers are unstable excited-state molecular complexes which occur onlyunder extreme conditions, such as those temporarily existing in specialtypes of gas discharge. Typical examples are the molecular bonds betweentwo rare gaseous atoms or between a rare gas atom and a halogen atom.Excimer complexes dissociate within less than a microsecond and, whilethey are dissociating, release their binding energy in the form ofultraviolet radiation. The dielectric barrier excimers in general emitin the range of from about 125 nm to about 500 nm, depending upon theexcimer gas mixture.

The above-described method of polymerizing a polymerizable material byexposing the polymerizable material to ultraviolet radiation in thepresence of the described photoreactor is useful for making a polymercoated fiber and a polymer-coated web. The fiber or web is coated with acomposition, such as is described hereinabove, comprising an admixtureof unsaturated polymerizable material and a photoreactor, and thecomposition on the fiber or web is irradiated with an amount ofradiation sufficient to cure the composition and form a coating on thefiber or web.

The present invention is further described by the examples which follow.Such examples, however, are not to be construed as limiting in any wayeither the spirit or the scope of the present invention. In theexamples, all parts are by weight, unless stated otherwise.

EXAMPLE 1

This example describes the preparation of the bimolecular photoreactor,2- p-(2-methyllactoyl)phenoxy!ethyl 1,3-dioxo-2-isoindolineacetate.

A 250 ml, three-necked, round-bottomed flask was fitted with a Dean andStark apparatus with condenser and two glass stoppers. The flask wascharged with 20.5 g (0.1 mole) of phthaloylglycine (Aldrich ChemicalCompany, Milwaukee. Wis.), 24.6 g (0.1 mole) of Darocur® 2959(α,α-dimethyl-α-hydroxy-4-(2-hydroxyethoxy)acetophenone, Ciba-GeigyCorporation, Hawthorne, N.Y.), 100 ml of benzene (Aldrich), and 0.4 g ofp-toluenesulfonic acid (Aldrich). The resulting mixture was heated atreflux temperature for three hours, after which time 1.8 ml (0.1 mole)of water was collected in the Dean and Stark apparatus. The solvent wasremoved to give 43.1 g of white powder. The powder was recrystallizedfrom 30 volume percent ethyl acetate in hexane (Fisher Scientific,Pittsburgh, Pa.) to give 40.2 g (93 percent yield) of a whitecrystalline powder having a melting point of 153°-4° C.

The expected structure was verified by infrared and nuclear magneticresonance analyses. The infrared spectrum of the powder was obtained asa Nujol mull and showed absorption maxima at 3440, 1760, 1680, and 1600cm⁻¹. The nuclear magnetic resonance data for the powder were asfollows:

¹ H NMR (CDCl₃): 1.64 (s), 4.25 (m), 4.49 (m), 6.92 (m), 7.25 (m), 7.86(m), 7.98 (m), 8.06 (m) ppm.

EXAMPLE 2

This example describes the preparation of the bimolecular photoreactor,2-hydroxy-2-methyl-4'- 2- p-(3-oxobutyl)phenoxy!ethoxy!propiophenone.The preparation was carried out in two steps.

A 100-ml round-bottomed flask was charged with 24.6 g (0.1 mole) ofDarcur® 2959, 20 ml of toluene (Aldrich), 11.9 g (0.1 mole) of thionylchloride (Aldrich), and 0.5 ml of pyridine (Aldrich). The flask wasfitted with a condenser and the reaction mixture was heated at refluxtemperature for two hours. The solvent was removed by distillation atreduced pressure (0.1 Torr) to yield a colorless solid which was usedwithout purification.

To a 250-ml, three-necked, round-bottomed flask fitted with a condenserand a magnetic stirring bar was added 17.6 g (0.1 mole) of4-(4-hydroxyphenyl)-butan-2-one (Aldrich), the chloro-substitutedDarocur® 2959 (α,α-dimethyl-α-hydroxy-4-(2-chloroethoxy)acetophenone)prepared as described above, 1.0 ml of pyridine, and 100 ml of anhydroustetrahydrofuran (Aldrich). The mixture was heated at reflux temperaturefor three hours and the solvent then was partially (about 60 volumepercent) removed under reduced pressure. The remaining mixture waspoured into ice water and extracted with two 50-ml aliquots of diethylether (Aldrich). The ether extracts were combined and dried overanhydrous magnesium sulfate. Removal of the solvent left 39.1 g of awhite solid. Recrystallization of the solid as described in Example 1gave 36.7 g (91 percent yield) of a white crystalline powder having amelting point of 142°-3° C.

The expected structure was verified by infrared and nuclear magneticresonance analyses. The infrared spectrum of the powder was obtained asa Nujol mull and showed absorption maxima at 3460, 1740, 1700, 1620, and1600 cm⁻¹. The nuclear magnetic resonance data for the powder were asfollows:

¹ H NMR (CDCl₃): 1.62 (s), 4.2 (m), 4.5 (m), 6.9 (m) ppm.

EXAMPLE 3

This example describes the preparation of the bimolecular photoreactor,p- (4-benzoylcyclohexyl)oxy!phenyl!-2-butanone.

To a 250-ml, two-necked, round-bottomed flask fitted with a condenserand a stopper was added 20.4 g (0.1 mole) of Irgacure® 184 (Ciba-Geigy)and 100 ml of anhydrous tetrahydrofuran. The mixture was stirred andcooled to ice/salt bath temperature while flushing the flask with argon.To the resulting solution was added slowly 20.0 g (0.15 mole) ofaluminum chloride (Aldrich) over a 40 minute period. The resultingmixture was stirred an additional 20 minutes. To the mixture then wasadded 17.6 g (0.1 mole) of 4-(4-hydroxyphenyl)butan-2-one. The newmixture was stirred overnight while being allowed to warm to ambienttemperature. The reaction mixture then was poured into ice water andextracted with three 50-ml portions of diethyl ether. Removal of theether gave 34.1 g of a white solid. Recrystallization of the solid from10 volume percent ethyl acetate in hexane gave 30.2 g (83 percent) of awhite crystalline powder having a melting point of 136°-8° C.

The expected structure was verified by infrared and nuclear magneticresonance analyses. The infrared spectrum of the powder was obtained asa Nujol mull and showed absorption maxima at 1760, 1740, 1620, and 1600cm⁻¹. The nuclear magnetic resonance data for the powder were asfollows:

¹ H NMR (CDCl₃): 2.10 (s), 2.70 (m), 6.80 (m), 6.92 (m), 8.42 (m) ppm.

EXAMPLE 4

This example describes the preparation of the trimolecular photoreactor,1,3-dioxo-2-isoindolineacetic acid, diester with2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone.

A 250-ml, two-necked, round-bottomed flask was fitted with a condenserand a Dean and Stark apparatus. The flask was charged with 41.0 g (0.2mole) of phthaloylglycine, 24.6 g (0.1 mole) of Darocur® 2959, 100 ml ofbenzene, and 3 ml of concentrated sulfuric acid (Fisher). The mixturewas heated at reflux temperature for three hours, after which time 3.6ml (0.2 mole) of water had been collected in the Dean and Starkapparatus. The solvent was removed from the reaction mixture to give61.8 g of a solid. The material was recrystallized as described inExample 1 to give 57.6 g (93 percent) of product having a melting pointof 168°-9° C.

The expected structure was verified by infrared and nuclear magneticresonance analyses. The infrared spectrum of the powder was obtained asa Nujol mull and showed absorption maxima at 1760, 1740, 1620, and 1600cm⁻¹. The nuclear magnetic resonance data for the powder were asfollows:

¹ H NMR (CDCl₃): 1.64 (s), 4.25 (m), 4.49 (m), 6.91 (m), 7.30 (m), 7.84(m), 7.98 (m), 8.06 (m) ppm.

EXAMPLE 5

This example describes the evaluation of the curing behavior ofadhesives containing the polymolecular photoreactors of Examples 1-4,inclusive, upon exposure to ultraviolet radiation from an excimer lamp.

An excimer lamp configured substantially as described by Kozelschatz andEliasson et at., supra, was employed and is shown diagrammatically inFIG. 1. With reference to FIG. 1, the excimer lamp 100 consisted ofthree coaxial quartz cylinders and two coaxial electrodes. The outercoaxial quartz cylinder 102 was fused at the ends thereof to a centralcoaxial quartz cylinder 104 to form an annular discharge space 106. Anexcimer-forming gas mixture was enclosed in the annular discharge space106. An inner coaxial quartz cylinder 108 was placed within the centralcylinder 104. The inner coaxial electrode 110 consisted of a wire woundaround the inner cylinder 108. The outer coaxial electrode 112 consistedof a wire mesh having a plurality of openings 114. The inner coaxialelectrode 110 and outer coaxial electrode 112 were connected to a highvoltage generator 116. Electrical discharge was maintained by applyingan alternating high voltage to the coaxial electrodes 110 and 112. Theoperating frequency was 40 kHz, the operating voltage 10 kV. Coolingwater was passed through the inner coaxial quartz cylinder 108, therebymaintaining the temperature at the outer surface of the lamp at lessthan about 120° C. The resulting ultraviolet radiation was emittedthrough the openings 114 as shown by lines 118. The lamp was used as anassembly of four lamps 100 mounted side-by-side in a parallelarrangement.

A standard adhesive mixture was prepared by mixing 90 parts by weight ofGenomer® D15OOB Difunctional Polyester Urethane Acrylate (Mader, BiddleSawyer Corporation, New York, N.Y.) and 9 parts of pentaerythritoltriacrylate (Polysciences, Inc., Warrington, Pa.). The mixture wasstirred by means of a magnetic stirring bar for 20 minutes at 80° C.

To aliquots of the standard adhesive mixture were added the compounds ofExamples 1-4, respectively. Two control mixtures were prepared usingcommercially available photoinitiators, Irgacure® 907(α,α-dimethyl-α-morpholino-4-methylthiophenylacetophenone or 2-methyl-1-4-(methylthio)phenyl!-2-morpholinopropanone-1, Ciba-Geigy) as Control A,and Darocur® 2959 as Control B. In each case, the amount ofphotoinitiator or photoreactor added was 1 part. Each resulting mixturewas stirred thoroughly. A few drops of each mixture were placed on ametal plate (Q-Panel Company, Cleveland, Ohio) and drawn down to a filmhaving a thickness of about 0.6 mil (about 0.015 mm) by means of adraw-down bar (Industry Tech., Oldsmar, Fla.). Each film then wasexposed to 222 nanometer (nm) ultraviolet radiation emitted by a KrCl*excimer lamp for a period of time sufficient to cure the film(through-cure time).

A film of adhesive was deemed cured completely, i.e., through the entirethickness of the film, when it passed the scratch test; see, e.g., M.Bralthwaite et at., "Chemistry & Technology of UV & EB Formulation forCoatings, Inks & Paints," Vol. IV, SITA Technology Ltd., London, 1991,pp. 11-12. The results are summarized in Table 1.

                  TABLE 1                                                         ______________________________________                                        Summary of Through-Cure Times With                                            Constant Photoreactor Concentration                                           Photoreactor                                                                              Through-Cure Time (Sec.)                                          ______________________________________                                        Control A   15.0                                                              Control B   12.4                                                              Example 1   2.0                                                               Example 2   3.2                                                               Example 3   4.6                                                               Example 4   2.2                                                               ______________________________________                                    

EXAMPLE 6

The procedure of Example 5 was repeated with varying concentrations ofphotoreactor. The amount of pentaerythritol triacrylate was decreased asrequired to provide 100 parts of control photoinitiator- orphotoreactor-containing adhesive. The results are summarized in Table 2(the data for a control photoinitiator or photoreactor concentration of1 percent are from Example 1).

                  TABLE 2                                                         ______________________________________                                        Summary of Through-Cure Times                                                 With Varying Photoreactor Concentrations                                             Through-Cure Time (Sec.)                                               Photoreactor                                                                           1 Percent 2 Percent 3 Percent                                                                             4 Percent                                ______________________________________                                        Control A                                                                              15.0      11.0      8.0     5.0                                      Control B                                                                              12.4      7.4       5.8     4.0                                      Example 1                                                                              2.0       1.4       0.9     0.5                                      Example 2                                                                              3.2       2.6       1.9     1.1                                      Example 3                                                                              4.6       3.9       2.7     2.0                                      Example 4                                                                              2.2       1.6       1.0     0.6                                      ______________________________________                                    

While the data in Tables 1 and 2 clearly demonstrate the remarkableimprovements in cure rates which are achieved with the polymolecularphotoreactors of the present invention, the data in Table 2 were plottedas photoreactor concentration versus through-cure time. The resultingplots, shown in FIG. 2, dramatically illustrate such remarkableimprovements.

EXAMPLE 7

A series of experiments was carried out as described in Example 5, usingonly Control B and the polymolecular photoreactor of Example 1 in orderto determine the effect of film thickness on through-cure times. In eachcase, the concentration of control photoinitiator or photoreactor was 4weight percent. The results are summarized in Table 3 (the data for afilm thickness of 0.6 mil are from Table 1).

                  TABLE 3                                                         ______________________________________                                        Summary of Through-Cure Times With Varying FiIm Thicknesses                   Film Thickness      Through-Cure Time (Sec.)                                  Mils   mm           Control B Example 1                                       ______________________________________                                        0.6    0.015        4.0       0.5                                             1.0    0.025        6.1       0.8                                             2.0    0.051        14.2      1.4                                             3.0    0.076        21.0      2.0                                             ______________________________________                                    

Regardless of the film thickness employed, the polymolecularphotoreactor of Example 1 clearly provided much faster curing rates. Inorder to better visualize the extent of improvement and any trends whichmay be present, the data of Table 3 were plotted as film thickness inmils versus through-cure times. The plots are shown in FIG. 3. While itis evident that film thickness affects through-cure time approximatelylinearly in each case, the rate of increase with increasing filmthickness for the control photoinitiator is much greater than for thepolymolecular photoreactor of Example 1.

It may be noted that, because of the high molar absorptivity of thepolymolecular photoreactors of the present invention, filmthickness/cure limitations may be observed with very thick filmthicknesses. For example, a 25-mil (about 0.64-mm) adhesive filmcontaining the photoreactor of Example 1 remained tacky on the sideadjacent to the metal plate supporting the film, even though the uppersurface, or top of the film, passed the scratch test.

EXAMPLE 8

The procedure of Example 1 was repeated with Control A, Control B, andthe photoreactor of Example 1 in order to test the curing behavior ofthe films upon exposure to the radiation from another ultraviolet lightsource. In this case, a 550-watt, wide spectrum emission, Hanovia mediumpressure mercury lamp (Hanovia Lamp Co., Newark, N.J.) was employed inplace of the excimer lamp. The distance from the lamp to the samplebeing irradiated was about 16 inches (about 41 cm). The results aresummarized in Table 4.

                  TABLE 4                                                         ______________________________________                                        Summary of Results with Medium Pressure Mercury Lamp                          Photoreactor Through-Cure Time                                                ______________________________________                                        Control A    60 seconds                                                       Control B    90 seconds                                                       Example 1    15 seconds                                                       ______________________________________                                    

The superiority of the polymolecular photoreactors of the presentinvention over known photoinitiators is clear, even when the radiationis not the essentially monochromatic emission which is characteristic ofan excimer lamp. The effective tuning of the polymolecular photoreactorfor a specific wavelength band permits the photoreactor to moreefficiently utilize any radiation in the emission spectrum of theradiating source corresponding to the "tuned" wavelength band, eventhough the intensity of such radiation may be much lower than, forexample, radiation from a narrow band emitter such as an excimer lamp.In other words, the effectiveness of the polymolecular photoreactor ofthe present invention is not dependent upon the availability or use of anarrow wavelength band radiation source.

EXAMPLE 9

Finally, the procedure of Example 5 was repeated using simple mixturesof sensitizer and photoinitiator. Two mixtures were studied. The first(Mixture A) consisted of Control A and phthaloylglycine, each beingpresent at a level in the adhesive of 1 weight percent. The secondmixture (Mixture B) consisted of Control B and phthaloylglycine: again,each component was present at a level of 1 weight percent. The resultsare summarized in Table 5.

                  TABLE 5                                                         ______________________________________                                        Summary of Results with Mixtures of Sensitizer and Photoinitiator             Mixture     Through-Cure Time                                                 ______________________________________                                        A           12.8 seconds                                                      B           10.1 seconds                                                      ______________________________________                                    

It will be remembered from Table 1 of Example 5 that the through-curetimes for Controls A and B at levels of 1 weight percent were 15.0 and12.4 seconds, respectively. It likewise will be remembered that thethrough-cure time for the bimolecular photoreactor of Example 1, alsopresent at a level of 1 weight percent, was 2.0 seconds. Given the factthat each of the components in the mixtures summarized in Table 5 waspresent at a level of 1 weight percent, it is evident that mixtures ofthe sensitizers and photoinitiators in these Examples are essentially nomore effective than the photoinitiator alone. Thus, the unique resultsobtained with the polymolecular photoreactors of these Examples weredependent upon the covalent bonding of the sensitizer to the freeradical-generating photoinitiator. Nevertheless, it is believed thatphysical mixtures of the sensitizer and photoinitiator are capable ofresults better than those achievable with photoinitiator alone. It ispostulated that such mixtures may be optimized by improving the blendingand/or the amounts of the two components.

While the specification has been described in detail with respect tospecific embodiments thereof, it will be appreciated that those skilledin the art, upon attaining an understanding of the foregoing, mayreadily conceive of alterations to, variations of, and equivalents tothese embodiments. Accordingly, the scope of the present inventionshould be assessed as that of the appended claims and any equivalentsthereto.

What is claimed is:
 1. A polymer-coated fiber, produced by the processof:providing a fiber coated with a composition comprising an admixtureof unsaturated polymerizable material and a photoreactor, wherein thephotoreactor comprises a wavelength-specific sensitizer covalentlybonded to a reactive species-generating photoinitiator; and irradiatingthe composition on the fiber with an amount of radiation sufficient tocure the composition and form a coating on the fiber, wherein thephotoreactor is 2-p-(2-methyllactoyl)phenoxy!ethyl-1,3-dioxo-2-isoindolineacetate, havingthe following structure: ##STR1##
 2. A polymer-coated fiber, produced bythe process of:providing a fiber coated with a composition comprising anadmixture of unsaturated polymerizable material and a photoreactor,wherein the photoreactor comprises a wavelength-specific sensitizercovalently bonded to a reactive species-generating photoinitiator; andirradiating the composition on the fiber with an amount of radiationsufficient to cure the composition and form a coating on the fiberwherein the photoreactor is 2-hydroxy-2-methyl-4'- 2-p-(3-oxobutyl)phenoxy!ethoxy!propiophenone, having the followingstructure: ##STR2##
 3. A polymer-coated fiber, produced by the processof:providing a fiber coated with a composition comprising an admixtureof unsaturated polymerizable material and a photoreactor, wherein thephotoreactor comprises a wavelength-specific sensitizer covalentlybonded to a reactive species-generating photoinitiator; and irradiatingthe composition on the fiber with an amount of radiation sufficient tocure the composition and form a coating on the fiber wherein thephotoreactor is 4- p- (4-benzoylcyclohexyl)oxy!phenyl!-2-butanone,having the following structure: ##STR3##
 4. A polymer-coated fiber,produced by the process of:providing a fiber coated with a compositioncomprising an admixture of unsaturated polymerizable material and aphotoreactor, wherein the photoreactor comprises a wavelength-specificsensitizer covalently bonded to a reactive species-generatingphotoinitiator; and irradiating the composition on the fiber with anamount of radiation sufficient to cure the composition and form acoating on the fiber wherein the photoreactor is1,3-dioxo-2-isoindolineacetic acid diester with2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone, having thefollowing structure: ##STR4##
 5. A method of coating a fiber,comprising:providing a fiber coated with a composition comprising anadmixture of unsaturated polymerizable material and a photoreactor,wherein the photoreactor comprises a wavelength-specific sensitizercovalently bonded to a reactive species-generating photoinitiator; andirradiating the composition on the fiber with an amount of radiationsufficient to cure the composition and form a coating on the fiberwherein the photoreactor is 2-p-(2-methyllactoyl)phenoxy!ethyl-1,3-dioxo-2-isoindolineacetate, havingthe following structure: ##STR5##
 6. A method of coating a fiber,comprising:providing a fiber coated with a composition comprising anadmixture of unsaturated polymerizable material and a photoreactor,wherein the photoreactor comprises a wavelength-specific sensitizercovalently bonded to a reactive species-generating photoinitiator; andirradiating the composition on the fiber with an amount of radiationsufficient to cure the composition and form a coating on the fiberwherein the photoreactor is 2-hydroxy-2-methyl-4'- 2-p-(3-oxobutyl)phenoxy!ethoxy!propiophenone, having the followingstructure: ##STR6##
 7. A method of coating a fiber, comprising:providinga fiber coated with a composition comprising an admixture of unsaturatedpolymerizable material and a photoreactor, wherein the photoreactorcomprises a wavelength-specific sensitizer covalently bonded to areactive species-generating photoinitiator; and irradiating thecomposition on the fiber with an amount of radiation sufficient to curethe composition and form a coating on the fiber wherein the photoreactoris 4- p- (4-benzoylcyclohexyl)oxy!phenyl!-2-butanone, having thefollowing structure: ##STR7##
 8. A method of coating a fiber,comprising:providing a fiber coated with a composition comprising anadmixture of unsaturated polymerizable material and a photoreactor,wherein the photoreactor comprises a wavelength-specific sensitizercovalently bonded to a reactive species-generating photoinitiator; andirradiating the composition on the fiber with an amount of radiationsufficient to cure the composition and form a coating on the fiberwherein the photoreactor is 1,3-dioxo-2-isoindolineacetic acid diesterwith 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone, having thefollowing structure: ##STR8##
 9. A polymer-coated web, produced by theprocess of:providing a web coated with a composition comprising anadmixture of unsaturated polymerizable material and a photoreactor,wherein the photoreactor comprises a wavelength-specific sensitizercovalently bonded to a reactive species-generating photoinitiator; andirradiating the composition on the web with an amount of radiationsufficient to cure the composition and form a coating on the web,wherein the photoreactor is 2-p-(2-methyllactoyl)phenoxy!ethyl-1,3-dioxo-2-isoindolineacetate, havingthe following structure: ##STR9##
 10. A polymer-coated web, produced bythe process of:providing a web coated with a composition comprising anadmixture of unsaturated polymerizable material and a photoreactor,wherein the photoreactor comprises a wavelength-specific sensitizercovalently bonded to a reactive species-generating photoinitiator; andirradiating the composition on the web with an amount of radiationsufficient to cure the composition and form a coating on the web,wherein the photoreactor is 2-hydroxy-2-methyl-4'- 2-p-(3-oxobutyl)phenoxy!ethoxy!propiophenone, having the followingstructure: ##STR10##
 11. A polymer-coated web, produced by the processof:providing a web coated with a composition comprising an admixture ofunsaturated polymerizable material and a photoreactor, wherein thephotoreactor comprises a wavelength-specific sensitizer covalentlybonded to a reactive species-generating photoinitiator; and irradiatingthe composition on the web with an amount of radiation sufficient tocure the composition and form a coating on the web, wherein thephotoreactor is 4- p- (4-benzoylcyclohexyl)oxy!phenyl!-2-butanone,having the following structure: ##STR11##
 12. A polymer-coated web,produced by the process of:providing a web coated with a compositioncomprising an admixture of unsaturated polymerizable material and aphotoreactor, wherein the photoreactor comprises a wavelength-specificsensitizer covalently bonded to a reactive species-generatingphotoinitiator; and irradiating the composition on the web with anamount of radiation sufficient to cure the composition and form acoating on the web, wherein the photoreactor is1,3-dioxo-2-isoindolineacetic acid diester with2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone, having thefollowing structure: ##STR12##
 13. A method of coating a web,comprising:providing a web coated with a composition comprising anadmixture of unsaturated polymerizable material and a photoreactor,wherein the photoreactor comprises a wavelength-specific sensitizercovalently bonded to a reactive species-generating photoinitiator; andirradiating the composition on the web with an amount of radiationsufficient to cure the composition and form a coating on the web,wherein the photoreactor is 2-p-(2-methyllactoyl)phenoxy!ethyl-1,3-dioxo-2-isoindolineacetate, havingthe following structure: ##STR13##
 14. A method of coating a web,comprising:providing a web coated with a composition comprising anadmixture of unsaturated polymerizable material and a photoreactor,wherein the photoreactor comprises a wavelength-specific sensitizercovalently bonded to a reactive species-generating photoinitiator; andirradiating the composition on the web with an amount of radiationsufficient to cure the composition and form a coating on the web,wherein the photoreactor is 2-hydroxy-2-methyl-4'- 2-p-(3-oxobutyl)phenoxy!ethoxy!propiophenone, having the followingstructure: ##STR14##
 15. A method of coating a web, comprising:providinga web coated with a composition comprising an admixture of unsaturatedpolymerizable material and a photoreactor, wherein the photoreactorcomprises a wavelength-specific sensitizer covalently bonded to areactive species-generating photoinitiator; and irradiating thecomposition on the web with an amount of radiation sufficient to curethe composition and form a coating on the web, wherein the photoreactoris 4- p- (4-benzoylcyclohexyl)oxy!phenyl!-2-butanone, having thefollowing structure: ##STR15##
 16. A method of coating a web,comprising:providing a web coated with a composition comprising anadmixture of unsaturated polymerizable material and a photoreactor,wherein the photoreactor comprises a wavelength-specific sensitizercovalently bonded to a reactive species-generating photoinitiator; andirradiating the composition on the web with an amount of radiationsufficient to cure the composition and form a coating on the web,wherein the photoreactor is 1,3-dioxo-2-isoindolineacetic acid diesterwith 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone, having thefollowing structure: ##STR16##